1. Field of the Invention
The present invention relates to a method for determining the type of digital versatile discs (DVD). More particularly, the present invention relates to a method for distinguishing among a DVD read-only-memory (ROM), a recordable DVD and a re-writable DVD.
2. Description of the Related Art
Digital versatile discs (DVD) have already become one of the most common data storage media in most electronic devices. Originally, the DVDs are used for recording videos. Gradually, however, DVDs begin to save other forms of data such as computer programs and files in a personal computer. Since the conventional read-only disc cannot copy the programs and files, various types of recordable digital versatile discs have been developed. The most common types of DVD include:                1. DVD ROM (read only memory). In other words, this type of optical disc only reads but cannot record data.        2. Recordable DVD, which is categorized into DVD-R and DVD+R. Herein, R stands for “recordable.” As the name suggests, this type of optical disc can record data for one time.        3. Re-writable DVD, which is categorized into DVD-RW and DVD+RW. RW stands for “re-writable.” This type of optical disc can record data for multiple times and hence is the most convenient recording medium.        
facilitate the users, DVD manufacturers have introduced optical disc players that are compatible with all kinds of digital versatile discs. However, each type of DVD has different data reading and writing method. Hence, the first thing the DVD player has to do after an optical disc is inserted is to determine the type of the DVD. In other words, the DVD must be distinguished as a ROM DVD, a recordable DVD or a re-writable DVD.
Conventionally, the type of DVDs is determined in two stages. In the first stage, the amplitude of a focus error signal is used to distinguish between a re-writable DVD from a non-re-writable DVD. The focus error signal is produced, for example, by turning on the laser beam of the DVD player and then driving the pick-up head (PUlH) to move up and down. The amplitude of the focus error signal is proportional to the reflectivity of the optical disc. Since the re-writable DVD has the lowest reflectivity, the characteristic of small amplitude in the focused error signal can be used to identify a re-writable DVD.
FIG. 1 is a graph showing the trace of a focus error signal. As shown in FIG. 1, the focus error signal is the curve marked as 101. The line 102 indicates a limit for the ROM DVD and the recordable DVD and the line 103 is a limit for the re-writable DVD. When the peak-to-peak voltage of the focus error signal is smaller than the limiting value 103 of the re-writable DVD, it is enough to determine that the optical disc inside the player is a re-writable DVD.
After distinguishing a re-writable DVD from a non-re-writable DVD, in the second stage of the conventional method, the characteristic land pre-pit information in a DVD-R and a DVD-RW optical disc and the characteristic address in pre-groove information in a DVD+R and DVD+RW are utilized to distinguish between a ROM DVD and a recordable DVD. Since the optical disc has already been determined as either a re-writable DVD or not in the first stage, this is no longer necessary in the second stage. Consequently, if the land pre-pit information or the address in pre-groove information can be read from the optical disc, the disc is a recordable DVD; otherwise, it is a ROM DVD.
FIG. 2 is a flow chart showing the steps in a conventional method for determining the type of DVDs. As shown in FIG. 2, a laser beam is turned on and then the pick-up head is driven to move up and down to generate a focus error signal in step 202. Thereafter, the largest and the smallest amplitude of the focus error signal are detected in step 204. The peak-to-peak voltage of the focused error signal is checked to determine whether the voltage is smaller than a limiting value indicating the absence of an optical disc. If the peak-to-peak voltage of the focused error signal is smaller than the limiting value, it is determined that an optical disc player is not inserted in step 208.
If the peak-to-peak voltage of the focused error signal is greater than or equal to the limiting value indicating the absence of an optical disc, the peak-to-peak voltage is again checked to determine if it is smaller than a limiting value for a re-writable DVD. If yes, it is determined that the optical disc inside the player is a re-writable DVD in step 212.
After distinguishing a re-writable DVD from a non-re-writable DVD, a calibration and a tracking operation are carried out in step 214 to prepare for a subsequent data reading operation. In step 216, the inserted optical disc is checked to determine whether pro-pit information or pro-groove information can be read or not. If yes, it is determined that the inserted optical disc is a recordable DVD in step 218; otherwise, the inserted optical disc is a ROM DVD.
The conventional method of determining the type of optical discs has many drawbacks. Firstly, when the quality of the pick-up head is poor, the quality of the read-out focused error signal would also degrade (for example, there may be a shift in the signal amplitude). As a result, the probability of determination error is increased. Secondly, re-writable DVDs having exceptionally high reflectivity or ROM DVDs or recordable DVDs having exceptionally low reflectivity are occasionally produced, rendering more determination error. Thirdly, when the land pro-pit information or the address in pro-groove information is difficult to read due to hardware or firmware problems, recordable DVDs or re-writable DVDs can be erroneously determined to be a ROM DVD. Fourthly, the step of reading the land pre-pit information and the address in pre-groove information is in the middle section of a servo-on process. Therefore, the ROM DVD is determined after many steps. Furthermore, after determining the type of optical discs, the servo-on process must be re-activated before data can be read from the optical discs. Consequently, a lot of time is wasted.
All in all, a better method must be provided to overcome the drawbacks of the conventional method of determining the type of optical discs, increase the accuracy of the determination and shorten the time for such determination.